Permanent mold risering

ABSTRACT

A graphite mold has riser openings lined with an insulator extending around the periphery and substantially across the bottom of the openings. The bottom portion of the insulator is formed of facing sand and phenolic resin while the peripheral portion of the insulator is formed of a coarser backing sand and phenolic resin. The insulator is baked by residual heat in the mold and decreases in thickness from the bottom toward the top of the riser opening.

Elite States tent r 1 Germain et a1.

. Assignee:

Filed:

PERMANENT MOLD RISERING Inventors: Andrew Gerald Germain, Medinah, I1l.; Donald Ray Wiles, Muncie, Kans.

Amsted Industries V Chicago, Ill.

Dec. 22, 1971 App1.No.: 210,638

Incorporated,

US. Cl. ..l64/23, 164/33, 164/165 Int. Cl. ..B22c 9/12 Field of Search ..l64/21, 23, 27, 33,

References Cited UNITED STATES PATENTS 6/1959 Sylvesten. ..l64/27 1/1957 Sylvester ..249/56X [1 1 3,735,796 [451 May 29, 1973 2,819,501 1/1958 Sylvester ..l64/386 X 2,838,816 6/1958 Strom ..249/56 3,302,919 2/1967 Beetle et al ..249/56 3,480,070 1 H1969 Beetle et a1 ..249/56 X Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Walter L. Schlegel, Jr. and Ralph M. Faust [5 7 ABSTRACT A graphite mold has riser openings lined with an insulator extending around the periphery and substantially across the bottom of the openings. The bottom portion of the insulator is formed of facing sand and phenolic resin while the peripheral portion of the insulator is formed of a coarser backing sand and phenolic resin. The insulator is baked by residual heat in the mold and decreases in thickness from the bottom toward the top of the riser opening.

3 Claims, 1 Drawing Figure ticularly to a method of forming insulator linings for riser openings in permanent molds.

In prior art methods of making insulator linings for risers ingraphite molds used for the bottom pressure pouring of steel wheels, a resin-sand mixture was manually poured with a scoop around metal plugs which were positioned in riser holes in the graphite molds, the bottom of the riser openings being closed by core bakers. Such insulator liners and their manner of fabrication are shown in U.S. Pat. No. 2,838,8 16, issued June 17, 1958 and U.S. Pat. No. Re. 24,655, issued June 2, 1959. Several problems are inherrent in this prior art method of forming riser liners. First, considerable manpower' is required, and second the type of resin-sand mixture which may be used is limited by the fact that the plugs must be withdrawn from the mold and the resin-sand hazardous mixture must not offer too much resistance to their withdrawal. In other words, the mixture must be relatively weak at the time of plug removal. Additionally, after a casting is completed the metal risers and liners must be removed by automatic riser cleaners. The manual dispensing of the resin-sand mix around the plugs, because of visual difficulties and obnoxious gases, produces a non-uniform height of insulator liners, and the height of the liners is important because if such height is too low, the permanent graphite mold will be damaged by the liquid metal rising above the liner during pouring. To prevent this, the liners are generally made higher than necessary, but in these instances the portions of the resin-sand mix above the height of the liquid metal do not bake through, thus making later removal of the resin-sand mix more difficult. Still further, the noxious gases emitted from the riser openings make such manual dispensing not only extremely unpleasant but also hazardous to health.

It is extremely important that a draft be provided in the riser insulator such that the wall thickness of the insulator decreases toward the top of the mold. The reason forthis is that after a casting has solidified, the

mold cope is lifted and the metal in the riser must be torn away from the wheel as close to the wheel face as possible, thereby minimizing the clean up work in removing excess riser material from the wheel. It has been found that the cope may be lifted approximately 7 minutes after pouring, with the riser remaining intact and broken off from the wheelclose to the face thereof, because of the wedging action created by the draft in the riser insulator.

It is a primary object of this invention to provide a riser insulator for a permanent type mold which can be formed in the mold riseropenings without the use of plug inserts, which is baked by residual heat in the mold, and which diminishes any thickness from the bottom of the riser openings toward the top surface of the mold.

This and other objects will become apparent from the following disclosure and accompanying drawing wherein the single FIGURE is a fragmentary vertical sectional view through a riser opening of a graphite mold.

Referring to the drawing, the numeral 10 designates a portion of a permanent, preferably graphite, mold such as might be used for the casting of steel railway car wheels substantially as shown in the aforementioned U.S. patent. The mold has atop surface 12 and 2 a downwardly facing surface 14 which partially defines a casting cavity 16. The mold is also provided with one or more riser openings 18 lined with an insulator'liner generally indicated at 20. The liner 20 includes a pcripheral wall portion 22, which decreases in thickness from the bottom of the riser openings toward the top surface of the mold but preferably does not extend completely to the surface 12. The liner also includes a second portion 24 extending substantially across the bottom of the riser opening and forming a continuation of the downwardly facing casting surface 14.

The riser insulators are formed in a heated mold, the mold either having been preheated or still hot as it is being recycled in casting operations. When the mold is placed in the production line where the riser liner is to be formed, it has a natural temperature gradient of approximately 465 at the downwardly facing surface defining the top of the casting cavity and approximately 380 F at the top surface of the mold. A core baker 26-, shaped to conform to the contour of surface 14, is placed 'in the cavity under the riser opening 13, the core baker having a projection 28 which is smallerthan the riser opening 18 and extends slightly thereinto.

Although if desired, the entire liner may be formed of a backing sand-phenolic resin mixture, preferably a layer of fine facing sand is deposited across the bottom of the riser opening against the core baker 26, the sand having previously been mixed with about l k to 3 V2 percent by weight of a phenol formaldehyde resin binder. The facing sand may be either very fine silica or may be zircon, as well known in the foundry art. The remainder of the riser opening is then filled to the desired height with backing sand, a silica sand having coarser grains than those of the facing sand, which has previously been mixed with 1 r to 3 percent by weight of phenol formaldehyde resin binder. After a predetermined time which will depend on the liner thickness desired but which generally is approximately I k to 2 minutes, the unbaked sand is dumped and the baking core is removed from the casting cavity. There now remains in the mold riser opening, a riser insulator liner having a bottom portion 24 preferably formed of facing sand, and a peripheral portion 22 which de creases in thickness toward the top surface of the mold. The projecting portion 30 which was formed over portion 28 of the baking core is knocked out to provide a sprue having -a smaller cross section than the riser proper.

The riser insulator liner formed by the above described method will have a tensile strength of 450 to 600 pounds per square inch as compared to a tensile strength of 300 to 350 pounds per square inch for liners formed by the prior art plug method, thus affording greater protection and consequently longer life to the graphite mold and also assuring that the metal in the riser will be torn off the casting close to the top face thereof.

The advantages of the new process are that the riser insulators are equal in height thereby assuring that molten metal does not flow over the insulator and solidify against the graphite mold. Damage to the graphite is, therefore, decreased resulting in approximately a 25 percent savings in graphite consumption and a similar savings in the amounts of sand resin mix which must be used per mold. The new method has also resulted in the elimination of at least two men per 8 hour shift in wheel casting plants. The new method also permits the economical use of a facing sand mix at the bottom of the riser opening and a coarser back up sand mix for the peripheral portion of the riser openings.

We claim:

1. In a method of forming a riser insulator in a riser opening of a graphite mold having a top surface and a downwardly facing surface defining a casting cavity communicating with the opening, the steps of: heating the mold to a certain temperature; permitting the mold to cool in air until the downwardly facing surface is at a second certain temperature and the top surface is at a temperature lower than the second temperature; closing the riser opening with a core baker positioned in the mold cavity; filling the riser opening to a predetermined height with a mixture of sand and thermosetting resin; and after a predetermined period of time, dumping the loose sand-resin mixture from the opening and leaving in the riser opening an insulator lining having a wall diminishing in thickness from the downwardly facing wall toward the top wall of the mold.

2. The method of claim 1 wherein, before the riser opening is filled with the sand-resin mixture, a layer of fine facing sand and thermosetting resin is placed in the riser opening over the core baker.

3. In a method of forming a riser insulator in the riser opening of a permanent mold having a top surface and a downwardly facing surface partially defining a casting cavity communicating with the opening, the steps of closing the riser opening with a core baker positioned in the mold cavity, covering the core baker with a mixture of facing sand and thermosetting phenolic resin, filling the riser opening to a predetermined height with a mixture of backing sand and thermosetting phenolic resin, baking the sand-resin mixes by residual heat in the mold for a predetermined period of time, and dumping the uncured loose sand-resin mixture from the riser opening and leaving in the riser opening a liner having a thickness which is progressively less from the downwardly facing surface toward the top surface of the mold.

* t II 

2. The method of claim 1 wherein, before the riser opening is filled with the sand-resin mixture, a layer of fine facing sand and thermosetting resin is placed in the riser opening over the core baker.
 3. In a method of forming a riser insulator in the riser opening of a permanent mold having a top surface and a downwardly facing surface partially defining a casting cavity communicating with the opening, the steps of closing the riser opening with a core baker positioned in the mold cavity, covering the core baker with a mixture of facing sand and thermosetting phenolic resin, filling the riser opening to a predetermined height with a mixture of backing sand and thermosetting phenolic resin, baking the sand-resin mixes by residual heat in the mold for a predetermined period of time, and dumping the uncured loose sand-resin mixture from the riser opening and leaving in the riser opening a liner having a thickness which is progressively less from the downwardly facing surface toward the top surface of the mold. 